1. Field of the Invention
This invention relates to a method and an apparatus for advancing underground more than two cylindrical bodies one after another.
2. Description of the Prior Art
In the conventional methods and apparatuses for advancing underground more than two cylindrical bodies, underground cylindrical bodies have been arranged to be advanced either in a self-propelling manner or with a required reaction force for an advancing operation obtained from something other than the cylindrical bodies to be advanced. In accordance with the conventional self-propelling method, however, a self-propelling operation is impossible until two cylindrical bodies has been advanced underground. On the other hand, the conventional method of obtaining a required reaction force from something other than the cylindrical bodies has necessitated the use of a large reaction arrangement and a large advancing facility. The present invention is directed to the elimination of such shortcomings of the conventional methods and apparatuses.